Open Data supplied by Natural Environment Research Council (NERC)

Aanderaa Pressure Recorder Type TG-2A and WLR-5

Pressure recorder TG-2A (serial number 64) was used until the end of 1979. It was then returned to Aanderaa Instruments Limited who carried out modifications changing it to the specification of an Aanderaa WLR-5. Hence from 1980 onwards the instrument is known as Aanderaa WLR-5 (serial number 500).

The Aanderaa recorder uses a Digiquartz type 2-300a quartz crystal pressure transducer. The pressure sensor consists of a convoluted bellows linked to a 40kHz quartz crystal resonator coupled by piezoelectric action to an electronic resonator. The sensor pack is mounted in a low profile steel tripod frame 0.76m by 1.183m in size with the sensor level approximately 0.48m above the frame base. Data are recorded on to 0.25 inch magnetic tape on an Aanderaa data logger in the same case. A quartz crystal clock is used for controlling the sampling interval.

The data are recorded as 10 bit binary words in serial form with the frequency count from the sensor stored as the most and least significant counts. There is no temperature sensor. The tide gauge is usually deployed using a U-shaped mooring (i.e. buoy or pellet float to wire rope to tide gauge to ground line to anchor to wire rope to buoy), but W-shaped moorings are used in conjunction with either current meters or thermistor chains. A W-shaped mooring comprises pellet float to pellet line to sub-surface buoy to current meter or thermistor line to anchor weight to ground line to tide gauge to ground line to anchor weight to wire rope to surface buoy.

IOS Calibration and Data Processing of Off-Shore Tide Gauge Data

Calibration of pressure/frequency sensors and thermistors are carried out using the facilities and staff at I.O.S. Bidston with the exception of pre 1975 pressure/frequency sensors, which were calibrated in the pressure chamber at I.O.S. Wormley.

The data are copied from the logger magnetic tape to 9 track magnetic tape and disk. The data are either listed or plotted as an initial check. A program is then used to check the data from the temperature sensor channels, calculate and plot the temperature values and store them (if temperature sensor channels are available).

A second program performs a similar function for the pressure sensor channel, using the pressure frequency coefficient to convert each pressure frequency to the frequency at the reference temperature and calculating the pressures using the pressure frequency calibration. The data values, generally at 15 minute intervals, but occasionally at 10 minute intervals, of pressure are then plotted and stored. If waterhead is required, it may be computed by subtracting atmospheric pressure and applying the hydrostatic relation:-

Mooring Information

5 meters were deployed on the mooring.

The data from the upper middle and lower middle meters are not included as they were measuring inclination (every 30 seconds) rather than current velocity. In addition the meter anchor was a ballast frame which housed two pressure recorders and an acoustic release.